The present invention is related to an improved shielding system for a chamber in which plasma is created.
In a typical semiconductor manufacturing operation plasmas are frequently used for many purposes, for example, for etching of layers formed on semiconductor wafers or deposition of materials on semiconductor wafers. Process technologies such as anisotropic plasma etching are well-known, as are processes such as plasma enhanced chemical vapor deposition. In such equipment, the plasma is typically created in the chamber, and then applied to a wafer after exiting through an aperture in the chamber wall. Another typical semiconductor manufacturing operation in which plasma are used is an ion implantation operation. Specifically, plasma is formed in a source chamber of an ion implantation machine.
FIG. 1 is a photograph illustrating the inside of a chamber 100 within which the plasma is formed. The particular equipment depicted in FIG. 1 is a source chamber for an ion implantation tool supplied by Varian. A cover plate has been removed to allow viewing of the chamber for illustrative purposes. Each time a plasma is formed in the chamber, deposits are formed on the interior surfaces of the chamber. These deposits gradually accumulate, necessitating periodic interruption of the use of the equipment for preventive maintenance.
The chamber 100 shown in FIG. 1 has interior surfaces, including a top surface 102, a bottom surface 104, and a beam aperture 106 through which an ion beam exits the chamber 100. As depicted in FIG. 1, the top surface 102 is generally planar and holds a top magnet, which is partially covered by a top magnet cover 108. Likewise, the bottom surface 104 also holds a bottom magnet which is partially covered by a bottom magnet cover 110. Furthermore, the chamber 100 is in fluid communication with a vacuum pump such as, for example, a turbo pump which is used to create and maintain vacuum conditions in the chamber. The turbo pump is partially shielded from the plasma by a flange 112.
In the configuration depicted in FIG. 1, the manufacturer has included two shields 114 and 116 which are illustrated near the rear surface of the chamber. As the machine is operated, the deposits form on these shields, and the shields can be removed for cleaning.
FIG. 2 is a photograph illustrating the side wall 201 of the chamber of FIG. 1. FIG. 2 illustrates a sidewall of the chamber 100, together with numerous corners and curves 202, which are difficult to reach and clean effectively. It is not unusual for technicians to spend hours cleaning material that deposits on these walls between periodic or preventative maintenances.
FIG. 3 is a photograph illustrating the bottom wall 302 (also 104 in FIG. 1) of the chamber of FIG. 1. FIG. 3 illustrates one of the magnets 304 in the bottom surface of the chamber (the circular region) together with the shield 306 (also 110 in FIG. 1) which only partially surrounds the magnet 304. The shield also receives depositions from the plasma formed in the chamber, and also must be cleaned. As can be seen from this figures (FIG. 3), the original manufacturer-supplied source magnet cover 306 does not sufficiently protect the source magnet regions, which receive considerable depositions during normal operation. FIG. 3 also shows flange 308 (also 112 in FIG. 1) which is used to prevent the depositions from the plasma on or near the turbo pump.
FIG. 4 illustrates the area 400 near the source turbo pump (not shown). The source turbo pump is partially protected from depositions from the plasma by the flange 308. When the chamber is cleaned the area surrounding the source turbo pump collects any fluid used to clean the chamber and traps it in places from which it is essentially impossible to manually remove. As a result, the trapped fluids are removed by pumping the chamber down to a vacuum, and waiting for all of the accumulated fluid to evaporate. The combined cleaning and outgassing time for the chamber greatly extends the duration of preventive maintenance. Of course, during all of the period that the equipment is offline, products cannot be produced, creating a less than efficient operation.
There is therefore a need for an improved shielding system that adequately protects the internal surfaces as well as regions near the vacuum pump of a plasma chamber from depositions from the plasma.